The present invention relates to a package structure, for a semiconductor device, and more particularly, it relates to a package structure having radiation solder bumps and connection solder bumps on a back surface of the package structure.
A conventional semiconductor device includes a package for covering a semiconductor chip, a substrate having a main surface on which the semiconductor chip is formed and radiation solder bumps and connection solder bumps formed on the back surface of the substrate.
The radiation solder bumps are formed in the center area of the back surface of the substrate. The connection solder bumps are formed in the peripheral area which surrounds the center area of the substrate. The connection solder bumps are electrically connected to electrodes of the semiconductor chip through conductive lines formed in the substrate. Therefore, the connection solder bumps have a function of terminals for connecting the semiconductor device to an outside circuit.
When the semiconductor device is mounted on a circuit board, the semiconductor device is subjected to a heat treatment (it is called as a reflow step). The circuit board has radiation pads located in corresponding position to the radiation solder bumps and connection pads located in corresponding position to the connection solder bumps. The radiation solder bumps and connection solder bumps are melted by the heat treatment so that both of the solder bumps are connected and joined to the pads, respectively. Therefore, the semiconductor device is fixed on the circuit board.
Each of the connection solder bumps should be connected to one of the connection pads independently. Therefore, the connection solder bumps are formed with a predetermined pitch so that the adjacent connection solder bumps should not joined each other by the heat treatment (it is called as a solder bridge).
The radiation bumps which are not connected to the electrodes of the semiconductor chip are formed with the same pitch of the connection solder bumps. The heat energy generated by the semiconductor chip in the package is transferred to the circuit board through a thermal conduction part including the radiation bumps and radiation pads. The transferred heat energy is diffused in the circuit board and outgoing from the circuit board.
Since the radiation solder bumps are formed with the same pitch of the connection solder bumps, a cross sectional area of the thermal conduction part is relatively small and a coefficient of thermal conductivity thereof is low.
The present invention is done in consideration of the problems of the conventional semiconductor device. The object of the present invention is to provide a new and improved semiconductor device including radiation protrude electrodes which improve coefficient of thermal conductivity of the semiconductor device.
To solve the issues of the conventional semiconductor device, a package structure for a semiconductor device comprises a substrate having a main surface and a back surface, a semiconductor chip formed on the main surface of the substrate, a package covering the semiconductor chip, radiation protrude electrodes and connection protrude electrodes. The radiation protrude electrodes are formed on the back surface of the substrate in a chip area where said semiconductor chip is located. Each of the radiation protrude electrodes are formed with a first pitch so that the radiation protrude electrodes make one body joining layer when the package structure is subjected to a heat treatment. The connection protrude electrodes are formed on the back surface of the substrate in a peripheral area of the chip area. Each of the connection protrude electrodes formed with a second pitch which is larger than the first pitch so that the connection protrude electrodes stay individual when the package structure is subjected to a heat treatment.